This invention relates to a method and apparatus for varying locking rates of a differential gear system. The system includes a driven differential cage with two coaxial axle shaft gears retained in cylindrical cavities in the cage. The gears are coupled to each other via pairs of meshed compensating gears positioned in cavities parallel to the axle gears.
The invention provides a method of varying locking rates, and for its implementation of several suitable differential gear systems of the aforementioned type, that will permit the varying of locking rates with minimum effort. Preferably, the system should provide a high locking rate when there is minimal traction detected on one wheel and thus minimal torque would be transmittable to the wheels and provide a low locking rate when high torques are being transmittable to the wheels due to good traction conditions, the control of which is through simple means. The solution lies in a method characterized in the engagement of various groups of meshing compensating gears with both axle shaft gears. The compensating gears are independently rendered either effective or ineffective in order to generate a variable resultant radial and/or tangential force to be applied to the axle shaft gears. The force generates a variable frictional force, at least on the periphery of the axle gears, inside the cylindrical cavities.
Such a method of incrementally varying the locking rates is simple to control, especially automatically as a result of torque controlled incremental engagement of additional groups of compensating gears. The resultant radial force applied to the axle shaft gears relatedly reduces the braking force generated by the resultant radial forces applied to these gears. The potential variation of the locking rate can reach a magnitude of approximately 70% when only one group of the compensating gears is in power-mesh with the axle shaft gears, and it is reduced down to a level of approximately 20-30% when all groups of compensating gears are in power-mesh with the axle shaft gears. In this case the locking rate is ##EQU1## where T.sub.1 and T.sub.2 are the torque on the axle gears with T.sub.1 &gt;T.sub.2.
A different gear system based on this invention has a driven differential cage in which two coaxial axle shaft gears, meshing on their external peripheries, are retained in cylindrical cavities, where the gears are coupled to each other via meshed compensating gears on parallel axes. The present invention includes at least one of the compensating gears provided with two toothed areas of different pitch. One of the toothed areas is meshed with one of the axle shaft gears, and the other area with at least one compensating gear that is associated with the other axle shaft gear. Also, an axial support means enables varying engagement of the compensating gears which provides variable force on the axle shaft gears.
Due to compensating gear tooth design, it is possible to have the compensating gear groups engage or become effective in a sequential manner. Engagement of the compensating gears with each other and the respective axle gears is accomplished only after relative axial shift of the compensating gears, as a gap is present between adjacent meshing teeth which provides the gear backlash. As the gears move axially, closing the gap between adjacent teeth, the compensating gears are power meshed with one another to transfer torque between the axle shaft gears if they are axially aligned. This is based on the torque-controlled axial force applied to the compensating gears, which overcomes axial spring force which is capable of limiting or biasing the shifting. Specifically, with a uniform backlash design, springs of different preloads may be specified for the individual compensating gear pairs. When using springs of uniform spring rates and initial preloads, different degrees of backlash may be used. Different degrees of backlash may be accomplished by means of different center distances between the compensating gears and the respective axle shaft gear. Alternatively, it is possible to utilize different tooth shapes.
As an alternative to this automatic configuration, an external control may be provided for the axial shifting of the support means having face-side support surfaces for the compensating gears, e.g. by hydraulic means.
The tooth areas covered by this invention need not be symmetrical with each other. A different pitch of any kind for at least one of the compensating gears coupled with the axle shaft gears would be appropriate.
As explained above, the curve locking rates versus torque transmitted, as generated by automatic controls, has a digressive trend. With external controls it is certainly possible to obtain locking rate curves of a different shape.
The subject matter of this invention can be equally applied to different gear systems having axle shaft gears in the form of sun gears, or in the form of internal ring gears. Additionally, an unequal torque distribution is possible by using different diameter axle shaft gears.
In order to guarantee a low locking rate as required during load reversals, for the benefit of directional control automatically, it is intended to design the gear backlash for the individual compensating gear groups to become effective at this status, to be uniform and to be overcome, free of opposing forces, by axial tooth forces. This requires each of the compensating gears with support means with axially shifting face-side support surfaces, to have on the side opposing the support means, secondary axial stop faces with uniform spacing relative to the compensating gear, so that during torque reversal, a low locking rate is obtained immediately upon contact between all the compensating gears and these secondary support surfaces.
Accordingly, a differential according to this invention may also have compensating gears with unequal helix angles between their two tooth sections, without necessarily having opposite sense of inclination. Essentially, for its engagement with the associated compensating gear and the associated axle shaft gears of the group, it is the axial position of each compensating gear that is critical. There is only one axial position for each compensating gear at which a given tooth load is obtained for an engagement with the axle shaft gear to guarantee the same tooth loads on all compensating gears. Depending on the shift direction, any deviation from this position, i.e. any shifting of a compensating gear, will result either in the tooth flanks of the axle shaft gear and the shifted compensating gear being additionally compressed while the remaining compensating gears are simultaneously relieved and lifted out of mesh, or in the relief of the shifted compensating gear and an additional loading of the remaining compensating gears. Any change in the axial loading causes a change in the resultant radial forces applied to the axle shaft gears, which determines the locking rates of a differential gear of said configuration.
From the following detailed description taken in conjunction with the accompanying drawings and subjoined claims, other objects and advantages of the present invention will become apparent to those skilled in the art.